<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body {
            margin: 0;
        }

        .wrap {
            margin: 0 auto;
            width: 900px;
        }

        #header {
            height: 100px;
            background: #6cf;
        }

        #main {
            height: 500px;
            background: #ffcccc;
        }

        #footer {
            height: 80px;
            background: #99ccff;
        }

        #middle {
            width: 100%;
            float: left;
        }

        #left {
            width: 200px;
            height: 100%;
            background: #ccffff;
            float: left;
            margin-left: -100%;
        }

        #right {
            width: 200px;
            height: 100%;
            background: #ccffff;
            float: left;
            margin-left: -200px;
        }

        .content {
            height: 500px;
            margin: 0 200px;
        }
    </style>
</head>
<body>
<header id="header" class="wrap"></header>
<section id="main" class="wrap">
    <section id="middle">
        <div class="content">content</div>
    </section>
    <aside id="left">left</aside>
    <aside id="right">right</aside>
</section>
<footer id="footer" class="wrap"></footer>
</body>
</html>